COLUMBA. 375 



half-way along its ventral border. Posterior to it is a 

 triangular ischium with a large oval foramen (the ischiatic 

 foramen). From its anterior border there runs backwards 

 beside the edge of the ischium a long pubis. There is 

 no symphysis. Just above and posterior to the acetabulum 

 is a small facet, the antitrochanter, which articulates with the 

 trochanter of the femur. 



The hind-limb has a short femur ^ a small and vestigial 

 fibula^ but a large tibia to which are fused the proximal 

 tarsal bones, hence it is known as the tibio tarsus. This is 

 followed by another compound bone, consisting of the 



Fig. 269. — Diagram of a Fowl's Egg at Laying. 



(After Allen Thomson.) 



Blastoderm. 



Plug of White Yolk, 



Chalaza. 



Air-Chamber./ 



Shell. 



/ Albumen. 



Vitelline Membrane. 



distal tarsals and three metatarsals, which is known as the 

 tarsometatarsus. It forks into three processes at its distal 

 end, each of which bears a digit. A small bone on its 

 inner side is the first metatarsal, which bears the first digit. 

 The number of phalanges increases outwards from two to 

 five. The pigeon has therefore no fifth or outer toe, and 

 the first is opposable to the other three. 



In the hind-limb there can be recognised the same two 

 features as in the front-limb, />., the reduction in the 

 number of digits and the fusion of tarsals and metatarsals. 

 In the hind-limb there is, however, a further fusion of the 



